NAME

pathchk - check pathnames

SYNOPSIS

pathchk[-p] [-P]pathname...

DESCRIPTION

The pathchk utility shall check that one or more pathnames are valid (that is, they could be used to access or create a
file without causing syntax errors) and portable (that is, no filename truncation results). More extensive portability checks are
provided by the -p and -P options.

By default, the pathchk utility shall check each component of each pathname operand based on the underlying file
system. A diagnostic shall be written for each pathname operand that:

Contains any component longer than {NAME_MAX} bytes in its containing directory

Contains any component in a directory that is not searchable

Contains any byte sequence that is not valid in its containing directory

The format of the diagnostic message is not specified, but shall indicate the error detected and the corresponding
pathname operand.

It shall not be considered an error if one or more components of a pathname operand do not exist as long as a file
matching the pathname specified by the missing components could be created that does not violate any of the checks specified
above.

Contains any character in any component that is not in the portable filename character set

-P

Write a diagnostic for each pathname operand that:

Contains a component whose first character is the <hyphen> character

Is empty

OPERANDS

The following operand shall be supported:

pathname

A pathname to be checked.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of pathchk:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables the precedence of internationalization variables
used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

NLSPATH

[XSI]
Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

0

All pathname operands passed all of the checks.

>0

An error occurred.

CONSEQUENCES OF ERRORS

Default.

The following sections are informative.

APPLICATION USAGE

The test utility can be used to determine whether a given pathname names an existing
file; it does not, however, give any indication of whether or not any component of the pathname was truncated in a directory where
the _POSIX_NO_TRUNC feature is not in effect. The pathchk utility does not check for file existence; it performs checks to
determine whether a pathname does exist or could be created with no pathname component truncation.

The noclobber option in the shell (see the set special
built-in) can be used to atomically create a file. As with all file creation semantics in the System Interfaces volume of
POSIX.1-2008, it guarantees atomic creation, but still depends on applications to agree on conventions and cooperate on the use of
files after they have been created.

To verify that a pathname meets the requirements of filename portability, applications should use both the -p and
-P options together.

EXAMPLES

To verify that all pathnames in an imported data interchange archive are legitimate and unambiguous on the current system:

PROCESSING represents the code that is used by the application to use $path once it is verified that
$path.out works as intended.

The state of the noclobber option is unknown when this code is invoked and should be set on exit to the state it was in
when this code was invoked. (The reset variable is used in this example to restore the initial state.)

Note the usage of:

rm "$path.out" > "$path.out"

The pathchk command has already verified, at this point, that $path.out is not truncated.

With the noclobber option set, the shell verifies that $path.out does not already exist before invoking rm.

If the shell succeeded in creating $path.out, rm removes it so that the
application can create the file again in the PROCESSING step.

If the PROCESSING step wants the file to exist already when it is invoked, the:

rm "$path.out" > "$path.out"

should be replaced with:

> "$path.out"

which verifies that the file did not already exist, but leaves $path.out in place for use by PROCESSING.

RATIONALE

The pathchk utility was new for the ISO POSIX-2:1993 standard. It, along with the set-C(noclobber) option added to the shell, replaces the
mktemp, validfnam, and create utilities that appeared in early proposals. All of these utilities were attempts
to solve several common problems:

Verify the validity (for several different definitions of "valid") of a pathname supplied by a user, generated by an
application, or imported from an external source.

Atomically create a file.

Perform various string handling functions to generate a temporary filename.

The create utility, included in an early proposal, provided checking and atomic creation in a single invocation of the
utility; these are orthogonal issues and need not be grouped into a single utility. Note that the noclobber option also
provides a way of creating a lock for process synchronization; since it provides an atomic create, there is no race between
a test for existence and the following creation if it did not exist.

Having a function like tmpnam() in the ISO C standard is important in many
high-level languages. The shell programming language, however, has built-in string manipulation facilities, making it very easy to
construct temporary filenames. The names needed obviously depend on the application, but are frequently of a form similar to:

$TMPDIR/application_abbreviation$$.suffix

In cases where there is likely to be contention for a given suffix, a simple shell for or while loop can be used
with the shell noclobber option to create a file without risk of collisions, as long as applications trying to use the same
filename name space are cooperating on the use of files after they have been created.

For historical purposes, -p does not check for the use of the <hyphen> character as the first character in a
component of the pathname, or for an empty pathname operand.